ISTANBUL -Turkish commandos have arrested 14 pirates thought to be from Somalia off the coast of Oman and freed seven Yemeni sailors they were holding hostage, the army said Sunday.

A helicopter of the frigate Giresun, which operates with NATO forces in the region, spotted the boat Friday around 190 nautical miles from the Omani coast, the army said in a statement on its website.

Commandos stormed the boat and seized nine assault weapons, a rocket launcher and other materials, said the statement, which was accompanied by photographs showing the suspects with their arms in the air as the raid began.

Turkey has been a partner in the international campaign against Somali pirates and arms smugglers in the northern Indian Ocean since early 2009.

The International Maritime Bureau recorded 439 acts of piracy in the world last year, mainly in Somalia, the Gulf of Guinea and Southeast Asia.

Oceans Beyond Piracy, a specialist American observatory, estimated the economic cost of Somali piracy at nearly $7 billion (5.4 billion euros) last year, of which $2 billion was spent on military operations, equipment and armed guards.